mike stehr

Bought this for 50 bucks roughly 17 years ago. Used it for breadboarding lower watt tube amplifier circuits for years in stock form, with the original parts. A conversation regarding these units came up with a local retired AE. He'd been coming across them, rebuilding them and using the supplies around the bench. They can be handy for that sort of thing. I figured then I should go through my Heathkit PS-4, re-cap, check over the resistors, etc... To be honest, while it may not have been completely up to spec in stock form, it was close. All the tubes still tested strong according to my no-go gauge emission tester.

I notice the pair of 269EX you purchased only has two bolts for the end-bells. I bought a pair of those the single-ended parallel pentode 6AQ5 amplifier I built. They also only had two bolts for the end-bells. It may not be an issue with you to be of concern, but one of mine had a mechanical rattle/buzzing that was fixed by installing two more bolts in the end-bells.

It sort of depends on the amplifier... I used to use stepped attenuators as a passive volume control, even an TVC (autoformer) type volume control or just straight from a CD player with variable output. I have a 2A3 stereo SET amp that does rather well with a passive type volume control. But I have lower watt amplifiers, like a RH84 SEP EL84 amp, and some Magnavox mono 6V6 push-pull amplifiers that seem to require a linestage/preamplifier to get a little more grunt and to sound best. The Altec 345A amp I have needs a preamplifier or it'll sound thin with a lack of bass. I made a Zero Zone clone/copy of the grounded grid linestage. There is more gain and better bass with the GG linestage. The linestage has a neutral sound to my ears.

I like the look of heavily polished aluminum. Unfortunately, the aluminum oxidizes as fast as natural Cherry darkens. Using that fancy micro-crystalline Renaissance wax polish does prolong the aluminum from oxidizing. It works rather well actually. Being flat pieces, it wouldn't be difficult to sand/polish them out...but it's a bit of a chore. The best to me is have the pieces anodized. Then they won't oxidize and are more scratch resistant over raw aluminum.

MagneQuest Seth PP-2-A-3 Service manual (manualmachine.com)

Dean aka Crankysoldermeister...

I do...

I did hardwood flooring installs for a friend years ago, and I remember a couple we did with natural Cherry. The shade of natural Cherry darkens quickly...you would sand an area, walk away for 5 minutes, and it already went dark upon return. Looks nice, but a bit soft for flooring to me. Not good if one has a dog.

Were... The best (to me) sounding single ended 6BQ5/EL84 circuit is the RH84 that I cobbled up using James 6123HS universal OPTs.

Isn't the Zen amplifier patterned after an old General Electric single-ended console stereo amplifier? Without the triode strapping I would guess... I've had good results from the RH84 circuit. There are many 6BQ5/EL84 single-ended circuits to choose from online.

A local audio friend asked me once what sort of function generator I had. Some cheap Simpson 420 I replied, with a dodgy amplitude pot. Well, he replies back that you need something that puts out a real sine wave. Nonetheless, I ended up with a HP 654A test oscillator. Didn't think much of it, until I compared the two units on a scope. The Simpson 420 has sine waves that have little peaks on the top, like they tried to make that triangle wave look like a sine, but not quite... The Hewlett Packard puts out clean beautiful sine waves. While for most, a Chinese function generator will be perfectly adequate. The Simpson 420 still works fine after cleaning the amplitude pot, and the square wave function works/looks good on a scope.

6L6 for pass tubes, 0A2 regulator tubes, with a 6BH6 control tube.

Look Mom! No clip-leads! If one wants to breadboard amplifier circuits of lower voltage/current, (like quite a few of Maynard's circuits) a guy can pick up a Tube DC power supply to use to power up an amplifier circuit. Then one doesn't necessarily have to buy PS iron or PS components. You just set-up the board and lash up the heater supply and B+. 6.3 volts at 4 amps is plenty of current for a few common tubes. Unfortunately, the Heathkit PS-4 and other similar Heathkit power supplies are only good up to 400 volts at 100 milliamps. I have a Lambda tube PS that's only 300-350 volts, with current at 150-200 milliamps. I wish I had a tube supply at 600 volts with over 200 milliamps current, but they are probably hard to find and very expensive in this day in age. Even these lowly Heathkit power supplies are going for stupid money now.

They make nickel or chrome plated sink plugs/caps in smaller sizes. You can cover the hole with one if so desired...you may have to enlarge the diameter of the hole to fit the cap being they only get so small. Or a dummy screw if you have clearance.

If one can manage to flip the chassis over, you can use the stepped bit to de-burr the bottom side of the diameters drilled. Make sure the piece being drilled is strapped down to something, as the stepped bit can be rather aggressive. It's a bit more spendy, but I like using stainless screws.

Heyco PG-7.

12AX7 in a SRPP configuration. I can't even recall what SRPP means...series resistance push-pull? Series reactance push-pull? Totem pole... I ginned up a 6SL7 in SRPP to drive a 71A. It sounded nice. I would think it would drive a 45/2A3 as well.

I have a 331A, which I think is the same unit but without the mode switch or high pass filter. It is in good working order as it was acquired from a retired audio engineer. I have a HP 654A test oscillator as well. While it does have an issue, (dodgy range switch?) if you let the unit sit powered up for a few hours it will work fine and puts out some beautiful sine waves. I'm currently trying to revive a HP model 205AG audio signal generator, which is an older Navy unit. Like you mention, the older HP distortion analyzers are good for use with tube amplifiers.

"Pure hand-made, the whole machine is welded with scaffolding." Must be a tall amplifier...

McIntosh MC275 MK VI Clone | Audiokarma Home Audio Stereo Discussion Forums

The evaluation board for TI 3255 has a reset toggle switch if I recall...